/*
 Copyright (c) 2007, 2010, Oracle and/or its affiliates. All rights reserved.
 

  The MySQL Connector/J is licensed under the terms of the GPLv2
  <http://www.gnu.org/licenses/old-licenses/gpl-2.0.html>, like most MySQL Connectors.
  There are special exceptions to the terms and conditions of the GPLv2 as it is applied to
  this software, see the FLOSS License Exception
  <http://www.mysql.com/about/legal/licensing/foss-exception.html>.

  This program is free software; you can redistribute it and/or modify it under the terms
  of the GNU General Public License as published by the Free Software Foundation; version 2
  of the License.

  This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
  without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  See the GNU General Public License for more details.

  You should have received a copy of the GNU General Public License along with this
  program; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth
  Floor, Boston, MA 02110-1301  USA

 */

package com.mysql.jdbc;

import java.sql.SQLException;
import java.util.Properties;

/**
 * Implement this interface to be placed "in between" query execution, so that
 * you can influence it. (currently experimental).
 * 
 * StatementInterceptors are "chainable" when configured by the user, the
 * results returned by the "current" interceptor will be passed on to the next
 * on in the chain, from left-to-right order, as specified by the user in the 
 * JDBC configuration property "statementInterceptors".
 * 
 * @version $Id: $
 */

public interface StatementInterceptor extends Extension {

	/**
	 * Called once per connection that wants to use the interceptor
	 * 
	 * The properties are the same ones passed in in the URL or arguments to
	 * Driver.connect() or DriverManager.getConnection().
	 * 
	 * @param conn the connection for which this interceptor is being created
	 * @param props configuration values as passed to the connection. Note that
	 * in order to support javax.sql.DataSources, configuration properties specific
	 * to an interceptor <strong>must</strong> be passed via setURL() on the
	 * DataSource. StatementInterceptor properties are not exposed via 
	 * accessor/mutator methods on DataSources.
	 * 
	 * @throws SQLException should be thrown if the the StatementInterceptor
	 * can not initialize itself.
	 */
	
	public abstract void init(Connection conn, Properties props) throws SQLException;

	/**
	 * Called before the given statement is going to be sent to the
	 * server for processing.
	 * 
	 * Interceptors are free to return a result set (which must implement the
	 * interface com.mysql.jdbc.ResultSetInternalMethods), and if so,
	 * the server will not execute the query, and the given result set will be
	 * returned to the application instead.
	 * 
	 * This method will be called while the connection-level mutex is held, so
	 * it will only be called from one thread at a time.
	 * 
	 * @param sql the SQL representation of the statement
	 * @param interceptedStatement the actual statement instance being intercepted
	 * @param connection the connection the statement is using (passed in to make
	 * thread-safe implementations straightforward)
	 * 
	 * @return a result set that should be returned to the application instead
	 * of results that are created from actual execution of the intercepted 
	 * statement.
	 * 
	 * @throws SQLException if an error occurs during execution
	 * 
	 * @see com.mysql.jdbc.ResultSetInternalMethods
	 */

	public abstract ResultSetInternalMethods preProcess(String sql,
			Statement interceptedStatement, Connection connection)
			throws SQLException;

	/**
	 * Called after the given statement has been sent to the server
	 * for processing.
	 * 
	 * Interceptors are free to inspect the "original" result set, and if a
	 * different result set is returned by the interceptor, it is used in place
	 * of the "original" result set. (the result set returned by the interceptor
	 * must implement the interface
	 * com.mysql.jdbc.ResultSetInternalMethods).
	 * 
	 * This method will be called while the connection-level mutex is held, so
	 * it will only be called from one thread at a time.
	 * 
	 * @param sql the SQL representation of the statement
	 * @param interceptedStatement the actual statement instance being intercepted
	 * @param connection the connection the statement is using (passed in to make
	 * thread-safe implementations straightforward)
	 * 
	 * @return a result set that should be returned to the application instead
	 * of results that are created from actual execution of the intercepted 
	 * statement.
	 * 
	 * @throws SQLException if an error occurs during execution
	 * 
	 * @see com.mysql.jdbc.ResultSetInternalMethods
	 */
	public abstract ResultSetInternalMethods postProcess(String sql,
			Statement interceptedStatement,
			ResultSetInternalMethods originalResultSet,
			Connection connection) throws SQLException;
	
	/**
	 * Should the driver execute this interceptor only for the
	 * "original" top-level query, and not put it in the execution
	 * path for queries that may be executed from other interceptors?
	 * 
	 * If an interceptor issues queries using the connection it was created for,
	 * and does not return <code>true</code> for this method, it must ensure 
	 * that it does not cause infinite recursion.
	 * 
	 * @return true if the driver should ensure that this interceptor is only
	 * executed for the top-level "original" query.
	 */
	public abstract boolean executeTopLevelOnly();

	/**
	 * Called by the driver when this extension should release any resources
	 * it is holding and cleanup internally before the connection is
	 * closed.
	 */
	public abstract void destroy();
}